1. Field of the Invention
The present invention relates to secondary oil recovery by waterflooding. Particularly, the present invention relates to a method and/or a hardware implementation of a method for controlling well injection pressures for at least one well injector used for secondary oil recovery by waterflooding. The control method additionally detects and appropriately reacts to step-wise hydrofracture events.
2. Description of the Relevant Art
Waterflooding is a collection of operations in an oil field used to support reservoir pressure at extraction wells (“producers”) and enhance oil recovery through a system of wells injecting water or other fluids (“injectors”). The waterflooding process uses fluid injection to transport residual oil remaining from initial primary oil production to appropriate producers for extraction. In this manner, wells that have finished primary production can continue to produce oil, thereby extending the economic life of a well field, and increasing the total recovered oil from the reservoir.
Waterflooding is by far the most important secondary oil recovery process. Proper management of waterfloods is essential for optimal recovery of oil and profitability of the waterflooding operation. Improper management of waterfloods can create permanent, irreparable damage to well fields that can trap oil so that subsequent waterflooding becomes futile. When excess injector pressure is used, the geological strata (or layer) containing the oil can be crushed (or hydrofractured). The growth of such hydrofractures can cause a direct conduit from an injector to a producer, whereby no further oil is produced, and water is simply pumped in the injector, conducted through the hydrofractured conduit, and recovered at the producer through a process known as “channeling.” At this juncture, the injector is no longer useful in its function, and is now known as a failed, dead, or lost well.
Lost wells are undesirable for many reasons. There is lost time in drilling a new well, resulting in lost production time. There is additional cost for the drilling labor and materials. Finally, a portion of the reservoir is rendered unrecoverable using traditional economically viable recovery means.
In some well fields, wells are spaced as close as every 25 meters. When a significant fraction of these closely packed wells fail, the drilling resources available may be exceeded, in such case, a lost well is truly lost, because it may not be replaced due to failure of yet more other wells.
The method disclosed here provides important information regarding the maximum pressures that may be used on a given well to minimize growth of new hydrofractures. This information may be important for groundwater remediation to environmentally contaminated regions by operation in a predominantly steady state flow mode where little additional hydrofracturing will occur. Such additional hydrofracturing will be shown below to be a transient component of injector to producer flow and commensurate hydrofracture growth.
U.S. Pat. No. 6,152,226 discloses a system and process for secondary hydrocarbon recovery whereby a hydrocarbon reservoir undergoing secondary recovery is subject to a first and then at least a second gravity gradient survey in which a gravity gradiometer takes gradient measurements on the surface above the reservoir to define successive data sets. The differences between the first and subsequent gravity gradient survey yields information as to sub-surface density changes consequent to displacement of the hydrocarbon and the replacement thereof by the drive-out fluid including the position, morphology, and velocity of the interface between the hydrocarbon to be recovered and the drive-out fluid.
U.S. Pat. No. 5,826,656 discloses a method for recovering waterflood residual oil from a waterflooded oil-bearing subterranean formation penetrated from an earth surface by at least one well by injecting an oil miscible solvent into a waterflood residual oil-bearing lower portion of the oil-bearing subterranean formation through a well completed for injection of the oil miscible solvent into the lower portion of the oil-bearing formation; continuing the injection of the oil miscible solvent into the lower portion of the oil-bearing formation for a period of time equal to at least one week; recompleting the well for production of quantities of the oil miscible solvent and quantities of waterflood residual oil from an upper portion of the oil-bearing formation; and producing quantities of the oil miscible solvent and waterflood residual oil from the upper portion of the oil-bearing formation. The formation may have previously been both waterflooded and oil miscible solvent flooded. The solvent may be injected through a horizontal well and solvent and oil may be recovered through a plurality of wells completed to produce oil and solvent from the upper portion of the oil-bearing formation.
U.S. Pat. No. 5,711,373 discloses a method for recovering a hydrocarbon liquid from a subterranean formation after predetermining its residual oil saturation. Such a method would displace a hydrocarbon fluid in a subterranean formation using a substantially non-aqueous displacement fluid after a waterflood.